The present invention relates to an image data processing system which divides image data of an image of one page into segmental image data and processes the segmental image data at a high speed.
There is known an image data processing system for compressing and expanding image data at a high speed. In the image data processing system, image data of an image of one page is divided into segmental image data, and companders are provided respectively in association with the segmental image data. A conventional image data processing system will be described with reference to FIG. 7. In this figure, reference numeral 1 designates a micro processor unit (MPU); 2, a direct memory access controller (DMAC); 3, an image input terminal (IIT); 4, an image output terminal (IOT); 5, an image memory; 6-1, 6-2, . . . and 6-n, companders; 7, an image data bus; 8, an coded data memory; and 8-1, 8-2, . . . and 8-n, segmental memory areas for coded data storage. The image memory 5, which has a memory capacity of storing image data of one page, is called a page memory.
FIG. 8 is a diagram showing segmental images making up an image of one page. In the figure, reference numeral 20 designates an image of one page; 20-1, 20-2, . . . and 20-n, segmental images (in this instance, an image of one page is divided into an n number of segmental images). The image data processing system of FIG. 7 includes the companders, which are provided respectively in association with the segmental images. The compander 6-1 is employed for compressing and expanding the image data of the segmental image 20-1, and the compander 6-2, for compressing and expanding the image data of the segmental image 20-2.
The data coded by the companders are stored into the coded data memory 8. The memory area of the memory 8 is also divided into an n number of the segmental memory areas, which is equal to the number of segmental images. Those segmental areas are denoted as 8-1 to 8-n shown in FIG. 7. The segmental memory areas are made to correspond to the companders respectively, and store the data coded by the companders. If the segmental memory area 8-1 corresponds to the compander 6-1, it stores the data coded by the compander 6-1.
The operation of the image data processing system thus arranged will be described. Image data read by the IIT 3 is stored into the image memory 5. The image data is transferred from the image memory 5 to the companders 6-1 to 6-n where the data is compressed. The companders process, in a parallel manner, the image data of the narrow segmental memory areas resulting from division of the one-page image. Accordingly, the time taken for the companders to complete the image data processing is much shorter than that taken for a single compander to complete data processing of the image in the entire area of one page. The data coded by the companders are stored into the corresponding segmental memory areas, respectively. The data transfer is performed under control of the DMAC 2.
To output image data, the segmental image data are read out of the segmental memory areas and supplied to the corresponding companders where the data are expanded. The expanded image data are transferred to the image memory 5 where the image data are composed into the image data of one page. Thereafter, the image data of one page is transferred to the IOT 4 which in turn produces the image data in the visual form. Also in this case, it is noted that the expanding processings in the respective segmental areas concurrently proceed. Therefore, the processing speed is much higher than that of the expanding processing carried out by a single compander.
An example of the conventional technique as stated above is disclosed by Japanese Patent Unexamined Publication No. Sho. 62-176374.
The image data processing system thus far described involves such a problem that the image memory for coded data storage is inefficiently used, with a relatively large part of the memory area being left unused or empty.
FIG. 9 shows a set of diagrams for explaining states of data storage in the segmental memory areas 8-1 to 8-n. In the figure, character A designates a data storage area, and Z designates an empty area. Where the one-page image 20 is divided into the n number of segmental images, as shown in FIG. 8, the compression ratio of the image data depends on a degree of complexity of each segmental image. In a certain page, its segmental image 20-1 may be complex. In this case, the compression ratio of the segmental image is low. When the data is coded, the resultant data or coded data is large in amount. In another page, its segmental image 20-1 may be simple. In this case, the compression ratio is high, and the coded data is small in amount. Thus, it is almost impossible to predict the compression ratios of the image data of the respective segmental images.
For the above reason, the segmental memory area 8-1 must have a memory capacity large enough to store the coded data indicative of the segmental image which is most complex. Practically,, not all the segmental images can be most complex, though. Accordingly, relatively large areas Z are usually left empty, as shown in FIG. 9, in the segmental memory areas 8-1 to 8-n. Thus, use of the image memory for coded data storage is inefficient, with a relatively large part of the memory area being left empty. This inefficient use of the image memory becomes more remarkable as the number of segmental images is increased for high speed processing.